Principles for a purification tool for gas chromatography: Vapour Pressure Purification.

We have developed a method, Vapour Pressure Purification (VPP), for extraction and purification of samples for gas chromatography. The automated procedure starts with a liquid/liquid extraction using a conventional organic solvent. After centrifugation, an aliquot (1 mL) is transferred to a new vial and moved to an automated dynamic headspace system, incorporating both a heater for the vial and a position for thermal desorption (TD) tubes. Here the solvent is first evaporated at low temperature, having an empty tube in the TD tube position. Immediately after dryness the TD tube is exchanged with a tube with Tenax TA and the temperature is increased to 150 °C. This enables extraction and quantitative transfer of the high boilers to the TD tube which is subsequently transferred to the thermal desorber and analysed using GC/MS. The complete procedure, including vortex and centrifugation, may be automated, using up to 10 mL aqueous based samples and 2 - 4 mL solvent. This takes around 30 min. For more extreme liquid/liquid extraction ratios the extraction/centrifugation may be done manually and the collected solvent transferred to the autosampler vial. The method may be used for aqueous based- or food samples. The method has so far been developed for three different extraction solvents: dichloromethane, methyl‑tert‑butyl‑ether and hexane.